This invention relates to improvements in or relating to thermostatic mixer devices for hydraulic systems, which devices are intended to be fed by a cold water pipe and a warm water pipe and to deliver water at a predetermined intermediate temperature regulated by a thermostat, which is fed, for exemple, to the various fixtures of a bathroom.
More exactly the invention relates to those types of thermostatic mixers in which a thermometric element immersed in the water of regulated temperature produces the displacement of a throttling member which cooperates with inlet apertures for the cold and the warm water respectively, by modifying in opposite directions the free passages in such a way as to compensate the temperature variations of the regulated water.
With these types of thermostatic mixers, in case of a feeding pressure variation occurring in only one of the inlet pipes, this variation generates a variation of the ratio of the warm water flow to the cold water flow and consequently a variation of the temperature of the delivered water, and the thermometric element has to intervene with a corrective action which, however, is substantially delayed by the thermic inertia.
Now, considerable temporary reductions of the pressure frequently occur in the cold water pipes, especially in consequence of sudden large diversions of water, as for instance those which are caused by actuation of flowmeter valves. These sudden drops of the pressure are not transmitted to the associated warm water pipe because of the hydraulic accumulator effect of the accumulation water heaters which are used generally. Accordingly, when the pressure in the cold water pipe decreases, there occurs for a short but not negligible period of time a delivery of excessively hot water which may produce damage, even serious damage, for instance if at that time a shower is being used.
The reverse phenomenon, i.e. a decrease of the pressure in the warm water pipe, occurs less frequently, because generally no fixtures of high instantaneous consumption of water are inserted in these pipes, and anyhow the consequence of such decrease would be a delivery of water having a lower temperature, which may produce a certain inconvenience, but no damage.